1. Field of the Invention
The invention relates in general to hybrid powered vehicles including an internal combustion engine and an electric motor.
2. Description of Related Art
Recently, a variety of hybrid powered vehicles provided with an electric motor and/or an engine have been developed to tackle environmental pollution. The method for driving the hybrid powered vehicle is roughly classified into the following three methods. First, drive wheels are driven solely by an output of an electric motor connected to the drive wheels. Secondly, the vehicle is driven solely by an output of the electric motor, and an internal combustion engine connected to a power generator is used for power generation only. Thirdly, the engine and the electric motor are selectively connected to the drive wheels so that the output of the electric motor and the output of the engine can be transmitted to the drive wheels. For example, Japanese Patent Provisional Publication No. 6-17727 discloses the hybrid powered vehicle provided with the electric motor and the engine. When the engine is started by engaging a clutch disposed between the engine and the electric motor while the vehicle is driven solely by the electric motor, the output of the electric motor is increased in order to decrease the transmission of the torque to the drive wheels. This prevents the vehicle from being shocked by the start of the engine, and improves the driving characteristics of the vehicle.
In general, there is a change in the torque of the engine when the engine is started. In the case of the hybrid powered vehicle, the change in the torque is transmitted to the electric motor that drives the engine. In the vehicle disclosed by Japanese Patent Provisional Publication No. 6-17727, an output shaft of the power generator is connected directly to the drive wheels, and thus, the change in the torque is transmitted to a body of the vehicle through a wheel drive system. This may result in the vibrations of the vehicle, giving a driver an unpleasant feeling. Similarly, if the output shaft of the electric motor is connected directly to the wheel drive system and a vehicle driving power source including the electric motor can be set to a plurality of driving modes by changing the engagement state of friction devices, the shock caused by the change in the driving modes is transmitted to the body, resulting in the vibrations of the vehicle. The vibrations are contrary to driver's expectations, and deteriorate the driving characteristics of the vehicle.